I Does quantum physics predict all isotope decays

[bland]

I am particularly wondering about zircon, element 40. I notice that its isotopes decay by either electron emission positron emission or electron capture, and I was curious to know whether this is established experimentally or if quantum physics is able to predict which isotopes will decay via which method.

thx.

 

[mfb]

It has been measured, and it can also be calculated.
The masses of the isotopes tell you which processes are possible, and every possible process will happen with some probability. Quantum mechanics can predict the probabilities and lifetimes, although experimental results are often more precise.